BackgroundTriphalangeal thumb is a congenital anomaly with three phalanges of the thumb. The general incidence is 1 in 25.000. Clinical presentation can vary from a complete long finger like thumb to the presence of a delta shaped extra phalanx. The variance in presentation reflects in possible problems in e.g. devation, joints, muscles, and tendon insertions. The aim of the surgical treatment is to correct the deformity and create a functional thumb. In this study the long term follow up of treated patients with the different types of triphalangeal thumb was assessed.

Methods A total of 66 patients were treated in our hospital of which 40 were included. Appearance and functionality were scored by the patients using a visual analogue score with a maximum of 10. To assess objective thumb function range of motion, skin colour, nail deformity, joint instability and joint deviation were measured. Opposition was measured using the Kapandij scale. Grip, pinch strength and muscle strength of the thumb were assessed. Questionnaires (DASH and SF-36) were used to measure objective function and handicap.

Results The mean VAS scores the functionality of the thumb were 7.5 (range 1 – 10), the mean score for appearance was 6.0 (range 1.5 – 9.7). Flexion of the interphalangeal joint had a mean of 50 degrees, the mean for flexion in the metacarpal joint was 55 degrees. All patients had a stable metacarpophalangeal joint. Maximum deviation of the thumb was 25 degrees (mean 5 degrees). The Kapandji test had a mean score of 8 (range 4 – 10). Strength of opposition a was on average lower compared to a normal population. Mean scores for precision grip were on the same level as for a normal population.

Discussion Operative treatment for patients with a triphalangeal thumb provides a functional thumb although function is not restored to normal .